Thermometer



June 1, 1943. J. seYHWARTZ THERMOMETER Filed May 7, 1941 Patented June 1, 1943 THERMOMETER John Leonard Schwartz, Philadelphia, Pa., as-

signer to Philadelphia thermometer Company, Philadelphia, Pa., a copartnership composed et John Leonard Schwartz, Clarence Rossman, and Hugo Englehardt Application May 7, 1941, Serial No. 392,203

4 Ciaims. (01. 73-371) This invention relates to difierential thermometers.

During laboratory tests and research work, on bacteria, as well as on chemicai or other substances, a difierential thermometer is used for accurately determining temperatures, within certain ranges, at different degrees of temperature, involved in the work or tests.

One of the objects of my invention is to pro- Vide a difierential thermometer having that part of the stem, where the reading is to be taken, include a very fine mercury (or other fluid) bore, so as to have on an adjoining scaie, a range of a few degrees of calibration, with as much spacing between consecutive degrees, as is possible, and thus afford opportunity to have a greater number of scaie sub-division of each degree, into smaller fractions thereof, for direct observation.

Inasmuh as it is dsirable to add to or shorten the mercury column, so as to bring its top to corne, for a given temperature, Within the range Of the said fixed, finely divided scaie, on the stem, for the few degrees thereof, another object of my invention is to provide a reservcir which will be in open communication with the bore of the stem, for either receiving or suppiying the mercury or other bore fluid, when changing the c01- umn length, to bring its top where desired.

A further object is to locate said reservoir at the upper end 01 the main stem, where a continuation, as a tubular extension to the main stem and its bore, canproject up into the said reservoir, the walls of which Will then surround this stem extension and form an annular pocket in the lower part of said reservoir, where mer- Cury or other column fluid can lodge, When the thermometer is held upright.

Another object is to form said stem extension into a measuring device, by calibrating it into degrees, corresponding to those of the scale bew, but in order to have the stem extension degree markings much closer together and make use of a shorter stem extension, another object is to have the bore of this stem extension much ]arger in diameter than that of the fine bore, of the main stem below.

Another object is to have the said reservoir and the mercury column, under considerable gas pressure, in order to maintain the continuity of the fine mercury column of the thermometer, and in this connection, a further object is to have in the bore of the stem extension, between the graduated portion thereof and the main stem, an enlarged portion, serving as a co-axial chamber bu1b, so as to receive, for a short distance, the mercury durin the lower degrees of expansion,

and thus make a shorter thermometer possible, while at the same time, afiording an easier exit of the mercury from the thermometer bu1b, to reduce any shock that mght come from suddenly increasing the mercury temperature, in the bulb.

" With these and other objects which will hercinafter appear, one embodiment of my invention is illustrated in the drawing, the construction is described, its functioning is explained, and What I claim is set forth.

In the drawing,

Figure 1 is an upright elevation of a difi'erential thermometer, embodying my invention, and is shown in fragmental lengths partiy broken away to illustrate the inner construction.

Figure 2 .is an inverted elevation, partlybroken away, showing the upper, reservoir end of the thermometer, similar to thatshown in Figure l.

Figure 3 is an inclined sectional elevation of the upper portion, of the thermometer shown in Figure 1.

Figure 4 is et section taken on the line 44, of Figure 1.

Figure 5 is a section taken on the line 5--5, of Figure 1.

In the figures, IIJ is the difierential thermometer having the usual bu1b I I, containing the mercury I2, and I3 is the s'olid glass, main stem of the thermometer, having a bore I4. The lower portion I5, of the bore l4, next to bulb Il, is

enlarged. The upper portion I8, of the main stem I3, is calibrated to form a scale I 6*, and within the portion I6, of the stem, is a fine bore portion I1. It will be noticed that the individual degree markings, on the scale I6 are unusuaily far apart, permitting a greater number of subdivisions for small fractions of degrees. Although fifty sub-divsions per degree are shown, any number of sub-divisions per degree, can be made as desired.,bearing in mind their readability, With or without the use of a microscope.

Whiie the number of full degrees shown is five, any umber of degrees can be provided for.

Surmounting the main stem I3, and integral therewith, is the closed reservoir I8, shown cylindrical and co-axially, integral With the main stem l3." This reservdf may be of any other shape desired, and be difierently positioned. Running up into the reservoir I8, to near its top end [9, is an auxiliary tubular stem 20, integral With the stem l3, having its bore 2l continuous With the bore I4 below. Theupper end 22, of the bore 2|, opens into the reservoir l8. In the lower part of the reservoir l8, where the auxiliary stem 20 enters, there is formed an annulaLr pocket 23, where mercury, or other stem fluid can lodge, to be added to, when the mercury column is shortened, or drawn upon; When the said column is lengthened.

The bor 2|, of the auxiliary stem 28, has a portion in its lower part formed into a chamber 24, comparatively much larger in diameter than that of the bore 2l. From this chamber 24, to the upper end of the stem 20, the bore 2! is uniform in diameter, and its diameter is larger than that of the bore I, of stem portion l6. The stem 20 =has degree calibrations 25, shorter per degree than the degree spacing on the: sCale of the stem portion l5, on account of its-larger bore. Inasmuch as the calibrated stem 20 is to be used in measuring portions of mercury within its bore, and such portions of mercury need only approximate What is to be added to, or taken from, the main stem column, there is not so much need for fine sub-divisions, as there is on the stem portion l5, where th readings indicated, are more for fractional Changes in temperature, within a given range.

When marfufacturing the thermometer l0, the reservoir l8 is filled With some gas under considerable pressure, which is sealed in, to bear down on the mercury column in the stem portion l6.

With the construction above described, an operator is ab1e to add mercur to, or take it from, the main bore, of the thermometer, in the following manner: suppose he desires to shorten the mercury column, he then holds the thermometer upright and heats th bulb H carefully, and watches the column rise, until m'ercury enters as a small bead, in the bottom part of the chambar 24; then before it has had a chance to cool much, he joits this bead away from the mercury column, to cause it to lodge in the upper part of the chamber 24. Once he has succeded in doing this, he again heats the bulb Il, 'causing the long mercury column 'to rise and compress the small amount of gas in the chambr 24, forcing the said bead up into the bore of the calibrated part, of the auxiliary stem 20, as at l2 of Figur 3, where he can ascertain in degrees and 'parts theref, the amount of mercury he has thus dislodged from the main mercury column. After thus separating this portion of the 'mercur'y from the column, the bulb I l is further 'heated and the mercury portion l2* which is lodged in the calibrated part, of the auxiliary stem 20, is forced out into the reservoir l8, where it drops to the pocket 23. If now, the operator wants to draw ofi more mercury from the column, he repeats the operation, beginning by separating off another bead of mercury, which he forces, as above explained, into the reservoir [8.

If, on the other hand, he wants to add to the column of mercury, he first heats the bulb l I, and immediately inverts the thermometer to have the mercury drop from the pocket 23, into the end 19, of the reservoir, as shown in Figure 2, and cause the auxiliary stem end 22, to be immersed in mercury, then as the bulb Il cools, he observes how many degrees of mercury is sucked up into the bore 2 I, of the stem 21]. When he has thus sucked up the portion of mercury he wants to add to the column, he turns the thermometer right side up, With the drawn-in portion of mercury lodged in the tubular stem 29. By jolting, he causes this mercury portion to drop into the chamber 24, to be added to the mercury column of the main stem, at the same time, the confined gas is given a chance to get above the mercury and get in free communication With the gas in the reservoir [8.

Inasmuch as changes in the construction of the thrm0meter as shown and described, can be 'made Without departing from the spirit of my invention, I desire to include al] modifications theiedf which corne within the scope of the following claims.

I claim:

1. A difierential thermometer comprising in combination, a hollow bulb, a main stem, With a bore in said stem connected With the inside of said bulb, there being mercury or other exparidable fluid within said bore and said bulb, a lower portion to said bore, opening directly into said bulb, having a comparatively enlarged section,'an upper portion to said stem having an exceedingly fine length of bore, a scale adjoining said 1ast mentioned length of bore, having finely divided subdivisions per degree, and a closed reservoir at the top of said main stem in open communication With said bore, said reservoir being in 'liiie With said stem, an open ended, auxiliary tubular stem forming an extension to said main stem, running up into said reservoir, forming With the walls of said reservoir, an annular, surrounding pocket at the lower end of the said reservoir, for receiving an excess of the thermometer fluid, expelied from the open end of said auxiliary, tubular stem, said reservoir containing gas under pressure and an expanded portion to the bore of said auxiliary, tubular stem at its lower end, forming a chamber throush which portions of expandable fluid can pass between the main bore of the auxiliary, tubular stem and the bore in the main stem and allow any confined gas t0 arise above the expandable fluid portion dropped therein from above and corne in free communication With the gas in the reservoir. 2. A difierential thermometer comprising in combination a hollow bulb, a main stem having a bore opening into said bulb, there being an expandabie fluid within said bore and said bulb, the lower portion of said main stem bore having a comparatively enlarged section, an upper portion to said main stem having a length of bore With a reduced section, a first scale having finely sub-divided divisions per degree, adjoining said reduced section of bore, a closed reservoir at the upper end of said main stem, an open ended, auxiliary, tubular stem, forming an extension to said main stem, running up into said reservoir and spaced from the wa1ls thereof, whereby to form an anhular pocket about said stem extension, for the reception of thermometer fluid exuded from said extension, the bore of said auxiliary stem opening into said reservoir, and having a section at its lower part larger than that of the bore in the upper part of said main stem, and a second scale of degres next to said enlarged bore, of said auxiliary stem, the degree markings on said second sca1e being closer than the degree markings on said first scale.

3. A difierential thermometer comprising in combination a hollow bulb, a main stem having a bore opening into said bulb, there being an expandable fluid within said bore and said bulb, a portion of said main stem having a length of bore with a reduced section, a first sca]e having finely subdivided division per degree adjoining said reduced section of bore, a closed reservoir at the upper end of said main stem, an open ended, auxiliary, tubu1ar stem, forming an extension to said main stem, running up into said reservoir and spaced from the walls thereof, whereby to form an annular pocket about said stem extension, for the reception of thermometer fiuid exuded from said extension, the bore 01" said auxiliary stem opening into said reservoir, and having 21. section larger at its 1ower end than that of the bore in the upper part of said main stem, and a second scale of degrees next to said enlarged bore, of said auxiliary stem, the degree markings on said second scale being closer than the degree markings on said first scale.

4. A difierential thermometer comprising in combination a hollow bulb, a main stem having a said reduced section of bore, a closed reservoir' at the upper end of said main stem, containing gag under pressure, an open ended, auxifi'ary, tubular stem, forming an extension to said main stem, running up into said reservoir and snaced from the Walls thereof, whereby to form a-n annular pocket about said stem extension, for the reception of thermometer fiuid exuded from said extension, the bore of said auxiliary stem opening into said reservoir, and having et section larger at its lower end than that of the bore in the upper part of said.main stem, and a second scale of degrees next to said enlarged bore, of said auXiliary stem, the degree markings on said second scale being closer than the degree markings on said first sca1e.

JOHN LONARD SCHWARTZ. 

